Papers

ICMCTF2002 Session F4-2: Microstructural, Microanalytical and Imaging Characterization

Monday, April 22, 2002 1:30 PM in Room San Diego

Monday Afternoon

Start	Invited?	Item
1:30 PM		F4-2-1 TEM in Tribology ¹ S.V. Prasad, P.G. Kotula, J.R. Michael (Sandia National Laboratories) Tribology is a systems property that involves interactions within pairs of siding surfaces and the surrounding environment. Dynamic reactions between contacting sliding surfaces and the environment, transfer and backtransfer of material between sliding surfaces, subsurface deformations and phase transformations beneath the wear surfaces are known to occur during sliding contact. Microstructural and chemical analysis of wear surfaces is therefore crucial to the understanding of the wear mechanisms as well as to the development of tailored materials for specific tribological applications. This paper illustrates the crucial role of transmission electron microscopy (TEM) in analyzing the wear surfaces with examples from self-lubricating metal-matrix composites, diamond like nanocomposite coatings, and microelectromechanical systems (MEMS). Novel specimen preparation techniques, e.g. ultramicrotomy for TEM wear debris samples and focused ion beam (FIB) for preparing cross sections of wear scars, will be presented. ¹ Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
2:10 PM		F4-2-3 Deposition of TiN Thin Films on Si(100) by Unbalance Magnetron Sputtering W.-J. Chou, G.P. Yu, J.-H. Huang (National Tsing Hua University, Taiwan, ROC) Titanium nitride (TiN) films were deposited on Si(100) substrate using an unbalance magnetron sputtering (UBM) technique. The thickness of the TiN film was controlled and, from our previous study, the nitrogen partial pressure was selected as the variable parameter. The purpose of this study is to investigate the effect of nitrogen partial pressure on the structure and properties of TiN films. After deposition, the thin film structure was characterized by X-ray diffraction (XRD), cross-sectional transmission electron microscopy (XTEM), and field-emission-gun scanning electron microscopy (FEG-SEM). N/Ti ratios of the thin films were determined using both X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS). The resistivity of the TiN films was measured by a four-point-probe. The hardness of the thin films was determined using nanoindentation tests. An atomic force microscope (AFM) was used to measure the roughness of the thin films. The results showed that (111) was the dominant preferred orientation in the TiN films for most of the deposition conditions. Hardness values of TiN films were about 30 GPa. Hardness can be correlated to the (111) preferred orientation of the TiN film. The lowest resistivity of the TiN film was about 60 mW-cm.
2:30 PM		F4-2-4 Structural Evolution of Codeposited Zn-Cr Coatings Realized by Vacuum Evaporation P. Choquet, C. Scott, C. Olier, A. Lamandé, D. Chaleix (USINOR Research & Development, France) The application of a thin vacuum coating of Zn-Cr to steel plate greatly improves the product corrosion resistance. The Zn-Cr offers a better resistance to perforation corrosion than ZnNi electrolytic coatings and, in terms of cosmetic corrosion properties, it is at least the equal of Zn based coatings. In this work, Zn and Cr. were evaporated simultaneously using two e-beam guns to heat crucibles containing the pure metals. The metallic vapors generated are intermixed and pass through a specially designed aperture that assures homogeneous deposition at the surface of the steel substrate, which continuously advances. The source positions were adjusted to produce a coating with a chromium content, which decreases from the substrate interface to the external surface. This paper discusses the chemical and microstructural variations of these codeposited layers as a function of chromium content and substrate temperature. In order to improve the formability of these coated substrates, the deposition chamber has been designed in such way as to produce a thin precoat (<200nm) consisting of a ZnCr alloy with a high chromium concentration. This precoat exhibits partial epitaxy with the substrate grains and thus improves the coating adherence.
2:50 PM		F4-2-5 Planar X-ray Total Reflection Waveguide-resonator as a Base for New Thin Film Testing Instruments V.K. Egorov (Institute of Problem Microelectronics Technology RAS, Russia); E.V. Egorov, T.V. Bil'chik (Moscow Engeneering and Phisical Institute, Russia) Analysis of thin film coating are usually carried out by help of X-ray methods with a standard analytical equipment using, usually.However,X-ray methods of a thin film testing can be simplified, essentially, and the instruments can be cheapened,considerably,if the planar X-ray total reflection waveguide-resonator (PXWR) will be used for the formation of a target incident X-ray beam. The principle of PXWR work is connected with the X-ray interference standing wave (ISW) arising in the extending slit (clearance) between plane parallel dielectric reflectors for the angle area θ<θc (θc-critical angle of the total reflection). PXWR is working as a resonator for an X-ray beam propagation across the slit in the narrow its size interval, only. Low limit of the interval is almost not depended on a reflector material refractive index and an X-ray wavelength and is evaluated as 15 nm. Upper limit of it is defined by a coherence distance of a transportating radiation and a reflectors material density. Magnitudes of the size limit for the PXWR with quartz reflectors at the transportation of CuKα and MoKα radiations amount to 91 and 36 nm, accordingly. Main merits of PXWR are a high compression of an X-ray beam in the slit and a small attenuation of the beam intensity. Magnitude of the compresion is near 1000-10000 owing to the X-ray radiation trapping in the angle area δθin~2θc. Special technology preparation of PXWR permits to get on the waveguide outlet an X-ray beam with a small divergence δθout<<2θc. The design and construction of X-ray diffractometer and TXRF spectrometers equiped by PXWR units for the X-ray beam formation are discussed. The experimental data shown the high efficiency application of PXWR for the structural and chemical analysis of thin film coatings are presented. It is shown that PXWR may be used for total reflectivity measurements been usually carried out with an X-ray monochromator using.
3:10 PM		F4-2-6 Preparation and Characterization of sp² - bond Carbon Composite Coating with Exceptionally High Load-bearing Capacity and High Wear Resistance X.T. Zeng (Gintic Institute of Manufacturing Technology, Singapore); S. Zhang (Nanyang Technological University, Singapore); X.Z. Ding (Gintic Institute of Manufacturing Technology, Singapore); D.G. Teer (Teer Coatings Ltd., United Kingdom) Surface coatings for high load wear applications require a combination of high hardness and toughness as well as good adhesion. Carbon composite coatings have attracted special interest because of their low friction coefficients and low wear rates. Unlike the normal diamond-like carbon (DLC) coatings which consist of a mixed sp³ and sp² bonding structure and are usually highly stressed, an almost pure sp²-bond carbon composite coating was reported, which demonstrated exceptional high toughness and high wear resistance. This paper reports the preparation and characterization of such sp² -bond carbon composite coating. The coating samples were deposited under different conditions using unbalanced magnetron sputtering of both metal and graphite targets, and characterized with Raman spectroscopy, transmission electron microscopy, nanoindentation, scratch tests and pin-on-disc wear tests against alumina. The coating under the optimized deposition conditions showed high hardness (15GPa) and also high toughness, resulting in an exceptionally high load-bearing capacity (up to 3 GPa loading pressure without cracking) and low wear rate in the order of 10^-9 mm³.N^-1 .m^-1. The coating structure and the wear mechanism are discussed based on the Raman and TEM studies.
3:30 PM		F4-2-7 Evaluation Structure of Nb/NbC Multilayer Coatings I. Dahan, N. Fraga, J. Sariel, U. Admon, M.P. Dariel (Ben-Gurion University of the Negev, Israel) Abstract The present communication is concerned with the interdiffusion kinetics and the interface breakdown that take place in the Nb/NbC multilayer system as the result of thermal anneals in the 400-800°C temperature range. Within this temperature range carbon is the diffusing species. Carbon diffuses from the carbide layer into the adjacent Nb layer, depleting its concentration within the carbide, causing the nucleation and subsequent growth of an intermediate Nb₂C layer and decerasing the width of the original Nb layer. X-ray diffraction data allowed determining the changes that take place within the three phases, i.e., Nb, Nb₂C and NbC as a function of time. Examination of cross-sections of the multilayer specimens porovides further data regarding the evolution of the microstructure. The high defect content of the micro-thick, sputter-deposited layers stands behind the break-down of the multilayer structure at low temperature.
3:50 PM		F4-2-8 Deposition and Mechanical Properties of Ti-Si-N Coated Layer on WC-Co by RF Inductively Coupled Plasma-enhanced Chemical Vapor Deposition E.-A. Lee, I.-W. Park, J.-M. Yoo, K.H. Kim (Pusan National University, Korea) Ti-Si-N thin films were deposited on WC-Co substrates by a inductively coupled plasma (ICP) enhanced chemical vapor deposition technique using a gaseous mixture of TiCl4, SiCl4, N2, H2, and Ar. Deposition behaviors of Ti-Si-N film on the deposition parameters were investigated in this work. . The Si addition (up to 20 at. %) to TiN film caused the nanostructural changes such as grain size refinement, randomly oriented structure, and precipitates of silicon nitride in the TiN matrix. The Ti-Si-N films were believed to be codeposited in the form of nc-TiN/a-Si3N4 nanocomposite from our instrumental analyses. The microharness value of Ti-Si-N film increased with an increase of Si content up to about 10 at. %, but decreased again beyond this value. Our research has focused to find the reason why the higher Si content in Ti-Si-N films reduced the microhardness value again. The XPS analyses revealed that free Si started to be codeposited with silicon nitride phase, and the amount of codeposited free Si increased as the Si content of the film increased beyond 10 at.%.
4:10 PM		F4-2-9 The Structure and Thermal Stability of Titanium Aluminium Chromium Nitride Coatings Deposited by Closed Field Magnetron Sputter Ion Plating S. Yang, D.G. Teer (Teer Coatings Ltd., United Kingdom) TiAlCrN coatings have been deposited by closed field magnetron sputter ion plating on to M42 high speed steel, stainless steel and alumina substrates. The Ti and Al content was kept constant and a series of coatings was deposited while varying Cr content. The nitrogen was controlled using an optical emission monitor with feed back control. Some of the coatings were heat treated in air at 600°C and 900°C. The coating compositions and structures have been studied using XRD, GDOES, SEM-EDAX, TEM and HRTEM with special reference to the effects of the heat treatment. Minimal changes were produce in the coating structure by the heat treatments while the 3 hours at 900°C treatment produced a thin Chromium Aluminium Oxide layer at the surface. It can be concluded that these coatings have excellent thermal stability and should retain good wear resistant properties at high temperature.
4:30 PM		F4-2-10 Fatigue of Composite Coatings Based on Hard Oxide Ceramic and Chrome Carbide M.V. Kireitseu, V.L. Basenuk (Institute of Machine Reliability, Belarus) Fatigue and fracture of the Al-Al₂O₃-CrC, steel-Al₂O₃-CrC, steel-CrC coatings have been investigated by in situ experiments performed in a scanning electron microscope. Micromechanical models using arrays of internal or surface cracks have been developed. The models provide mechanics of deformation and failure for the coating. The models also reveal role of overloading in crack arrest, which may well be exploited in the safe design of toughened ceramics against fatigue. By this model in the paper is tried to explained a nature of fatigue in the composite. The trapped crack front resembles a collinear array of microcracks interspersed by grains rich in transformable precipitates. The model provides a reasonable explanation for the observed fatigue crack growth. A procedure similar to the one used in the analysis of the array of collinear cracks, based on complex potentials and dislocation formalism is also used to simulate fatigue of composite coatings based on anodic oxide ceramics and chrome carbide. Assuming power-law crack growth, it is found that the crack growth rate decreases with the applied stress intensity factor in the initial stage of fatigue crack growth. Depending on the applied load and the amount of transformation, the growth rate either goes through a minimum before increasing to the normal crack regime, or the rate continues to decrease until the crack is arrested. Initial overloads prior to cyclic loading are found to reduce significantly the crack driving force in post-overload fatigue crack growth. Indeed, an initial overload is found to cause crack arrest in a material with low transformation strength. For materials with high transformation strength, the initial overload has no beneficial effect on the endurance limit. Materials with transformation strength in the intermediate range show a substantial improvement in the endurance limit - typically a doubling of this limit by sufficient pre-fatigue overloading.